Remove theme picker #218

Job	Run time
Test 32-bit version	42s
Format - nightly toolchain	12s
Docs - stable toolchain (recent)	1m 33s
Test - 1.63.0 toolchain (minimal)	1m 59s
Test - 1.63.0 toolchain (recent)	1m 51s
Prepare	3s
WASM - stable toolchain	1m 57s
Test - stable toolchain (minimal)	55s
Test - stable toolchain (recent)	28s
Bench - nightly toolchain (recent)	34s
Lint - nightly toolchain (recent)	22s
Docs - nightly toolchain (recent)	49s
Test - nightly toolchain (minimal)	30s
Test - nightly toolchain (recent)	37s
	12m 32s

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